Experimental studies indicate that energy homeostasis to the circadian clock at the behavioral, physiological, and molecular levels, emphasize that timing of food intake may play a significant role in the development of obesity and central obesity. Therefore, resetting the circadian clock by circadian energy restriction via food intake in the morning or evening, may be used as a new approach for prevention of obesity, metabolic syndrome and related diseases. After ethical clearance and written, informed consent, free living subjects were included if they volunteered to take most of the total daily meals (approximately 2000 Kcal./day) in the evening (4 weeks) or morning (4 weeks). Of 22 adults, half were randomly selected by computer generated numbers to eat in the morning and the other half in the evening, after 8.00 PM. The eating pattern was changed after 4 weeks of intervention and a 4-week washout period, those who ate in the morning were advised to eat in the evening and vice versa. Validated questionnaires were used to assess food intakes, physical activity, and intake of alcohol and tobacco. Physical examination included measurement of body weight, height, and blood pressure (BP) by sphygmomanometer. Data were regularly recorded blindly, in all subjects at start of study and during follow-up. Blood samples were collected after an overnight fast for analysis of blood glucose and Hb1c. Feeding in the evening was associated with significant increase in body weight by 0.80 kg (P < .001), body mass index (BMI) by 0.30 kg/m2 (P < .001) and waist circumference by 1.13 cm (P < .05). Feeding the same amount of energy in the morning was not associated with any significant change in weight, BMI or waist circumference (P > .500). Lesser increases in all three variables were associated with AM versus PM feeding (P < .05). Systolic BP slightly increased on PM and decreased on AM feeding, with a difference between the two responses of 1.55 mmHg (P < .05). Fasting blood glucose was lower on AM than on PM feeding (74.86 vs. 77.95 mg/dl, paired t = 4.220, P < .001). Hb1C increased on PM feeding by 0.28 (from 4.45 to 4.73; t = 9.176, P < .001), but decreased on AM feeding by 0.077 (from 4.53 to 4.45; t = -6.859, P < .001). The difference in Hb1C response between AM and PM feeding is also statistically significant (t = -11.599, P < .001). Eating in the evening can predispose to obesity, central obesity and increases in fasting blood glucose and Hb1c that are indicators of the metabolic syndrome. By contrast, eating in the morning can decrease Hb1c and systolic BP, indicating that it may be protective against the metabolic syndrome.
Keywords: Food intake; circadian clock; metabolism; morning or evening eating.